title: Comprehensive characterisation of pulmonary and serum surfactant protein D in COPD.
abstract: BACKGROUND
  Pulmonary surfactant protein D (SP-D) is considered as a candidate biomarker for the functional integrity of the lung and for disease progression, which can be detected in serum. The origin of SP-D in serum and how serum concentrations are related to pulmonary concentrations under inflammatory conditions is still unclear.
  
  
  METHODS
  In a cross-sectional study comprising non-smokers (n=10), young--(n=10), elderly smokers (n=20), and smokers with COPD (n=20) we simultaneously analysed pulmonary and serum SP-D levels with regard to pulmonary function, exercise, repeatability and its quaternary structure by native gel electrophoresis. Statistical comparisons were conducted by ANOVA and post-hoc testing for multiple comparisons; repeatability was assessed by Bland-Altman analysis.
  
  
  RESULTS
  In COPD, median (IQR) pulmonary SP-D levels were lower (129(68) ng/ml) compared to smokers (young: 299(190), elderly: 296(158) ng/ml; p<0.01) and non-smokers (967(708) ng/ml; p<0.001). The opposite was observed in serum, with higher concentrations in COPD (140(89) ng/ml) as compared to non-smokers (76(47) ng/ml; p<0.01). SP-D levels were reproducible and correlated with the degree of airway obstruction in all smokers. In addition, smoking lead to disruption of the quaternary structure.
  
  
  CONCLUSIONS
  Pulmonary and serum SP-D levels are stable markers influenced by smoking and related to airflow obstruction and disease state. Smaller subunits of pulmonary SP-D and the rapid increase of serum SP-D levels in COPD due to exercise support the translocation hypothesis and its use as a COPD biomarker.
  
  
  BACKGROUND
  no interventional trial.
authors.affiliation: Department of Clinical Airway Research, Fraunhofer Institute for Toxicology and Experimental Medicine, Hannover, Germany.
authors.forename: Carla
authors.initials: C
authors.lastname: Winkler
authors.forename: Elena N
authors.initials: EN
authors.lastname: Atochina-Vasserman
authors.forename: Olaf
authors.initials: O
authors.lastname: Holz
authors.forename: Michael F
authors.initials: MF
authors.lastname: Beers
authors.forename: Veit J
authors.initials: VJ
authors.lastname: Erpenbeck
authors.forename: Norbert
authors.initials: N
authors.lastname: Krug
authors.forename: Stefan
authors.initials: S
authors.lastname: Roepcke
authors.forename: Gereon
authors.initials: G
authors.lastname: Lauer
authors.forename: Martin
authors.initials: M
authors.lastname: Elmlinger
authors.forename: Jens M
authors.initials: JM
authors.lastname: Hohlfeld
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D015415:Biomarkers / Q000097:blood; D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry / Q000166:cytology; D003124:Colorimetry; D003430:Cross-Sectional Studies; D005080:Exercise Test; D005260:Female; D005541:Forced Expiratory Volume; D005858:Germany; D006801:Humans; D008168:Lung / Q000378:metabolism* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D011237:Predictive Value of Tests; D020836:Protein Structure, Quaternary; D029424:Pulmonary Disease, Chronic Obstructive / Q000097:blood* / Q000209:etiology / Q000503:physiopathology; D037663:Pulmonary Surfactant-Associated Protein D / Q000097:blood* / Q000737:chemistry; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D012907:Smoking / Q000009:adverse effects / Q000097:blood*; D014797:Vital Capacity; D055815:Young Adult
chemical_list: D015415:Biomarkers; D037663:Pulmonary Surfactant-Associated Protein D